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Subject[PATCH v2 1/1] arm: topology: remove cpu_efficiency
Date
Remove the 'cpu_efficiency/clock-frequency dt property' based solution
to set cpu capacity which was only working for Cortex-A15/A7 arm
big.LITTLE systems.

I.e. the 'capacity-dmips-mhz' based solution is now the only one. It is
shared between arm and arm64 and works for every big.LITTLE system no
matter which core types it consists of.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---
arch/arm/kernel/topology.c | 132 ++-------------------------------------------
1 file changed, 4 insertions(+), 128 deletions(-)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 24ac3cab411d..15cc131ae387 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -30,69 +30,11 @@
#include <asm/cputype.h>
#include <asm/topology.h>

-/*
- * cpu capacity scale management
- */
-
-/*
- * cpu capacity table
- * This per cpu data structure describes the relative capacity of each core.
- * On a heteregenous system, cores don't have the same computation capacity
- * and we reflect that difference in the cpu_capacity field so the scheduler
- * can take this difference into account during load balance. A per cpu
- * structure is preferred because each CPU updates its own cpu_capacity field
- * during the load balance except for idle cores. One idle core is selected
- * to run the rebalance_domains for all idle cores and the cpu_capacity can be
- * updated during this sequence.
- */
-
#ifdef CONFIG_OF
-struct cpu_efficiency {
- const char *compatible;
- unsigned long efficiency;
-};
-
-/*
- * Table of relative efficiency of each processors
- * The efficiency value must fit in 20bit and the final
- * cpu_scale value must be in the range
- * 0 < cpu_scale < 3*SCHED_CAPACITY_SCALE/2
- * in order to return at most 1 when DIV_ROUND_CLOSEST
- * is used to compute the capacity of a CPU.
- * Processors that are not defined in the table,
- * use the default SCHED_CAPACITY_SCALE value for cpu_scale.
- */
-static const struct cpu_efficiency table_efficiency[] = {
- {"arm,cortex-a15", 3891},
- {"arm,cortex-a7", 2048},
- {NULL, },
-};
-
-static unsigned long *__cpu_capacity;
-#define cpu_capacity(cpu) __cpu_capacity[cpu]
-
-static unsigned long middle_capacity = 1;
-static bool cap_from_dt = true;
-
-/*
- * Iterate all CPUs' descriptor in DT and compute the efficiency
- * (as per table_efficiency). Also calculate a middle efficiency
- * as close as possible to (max{eff_i} - min{eff_i}) / 2
- * This is later used to scale the cpu_capacity field such that an
- * 'average' CPU is of middle capacity. Also see the comments near
- * table_efficiency[] and update_cpu_capacity().
- */
static void __init parse_dt_topology(void)
{
- const struct cpu_efficiency *cpu_eff;
- struct device_node *cn = NULL;
- unsigned long min_capacity = ULONG_MAX;
- unsigned long max_capacity = 0;
- unsigned long capacity = 0;
- int cpu = 0;
-
- __cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
- GFP_NOWAIT);
+ struct device_node *cn;
+ int cpu;

cn = of_find_node_by_path("/cpus");
if (!cn) {
@@ -101,9 +43,6 @@ static void __init parse_dt_topology(void)
}

for_each_possible_cpu(cpu) {
- const u32 *rate;
- int len;
-
/* too early to use cpu->of_node */
cn = of_get_cpu_node(cpu, NULL);
if (!cn) {
@@ -111,76 +50,15 @@ static void __init parse_dt_topology(void)
continue;
}

- if (topology_parse_cpu_capacity(cn, cpu)) {
+ if (topology_parse_cpu_capacity(cn, cpu))
of_node_put(cn);
- continue;
- }
-
- cap_from_dt = false;
-
- for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++)
- if (of_device_is_compatible(cn, cpu_eff->compatible))
- break;
-
- if (cpu_eff->compatible == NULL)
- continue;
-
- rate = of_get_property(cn, "clock-frequency", &len);
- if (!rate || len != 4) {
- pr_err("%pOF missing clock-frequency property\n", cn);
- continue;
- }
-
- capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;
-
- /* Save min capacity of the system */
- if (capacity < min_capacity)
- min_capacity = capacity;
-
- /* Save max capacity of the system */
- if (capacity > max_capacity)
- max_capacity = capacity;
-
- cpu_capacity(cpu) = capacity;
}

- /* If min and max capacities are equals, we bypass the update of the
- * cpu_scale because all CPUs have the same capacity. Otherwise, we
- * compute a middle_capacity factor that will ensure that the capacity
- * of an 'average' CPU of the system will be as close as possible to
- * SCHED_CAPACITY_SCALE, which is the default value, but with the
- * constraint explained near table_efficiency[].
- */
- if (4*max_capacity < (3*(max_capacity + min_capacity)))
- middle_capacity = (min_capacity + max_capacity)
- >> (SCHED_CAPACITY_SHIFT+1);
- else
- middle_capacity = ((max_capacity / 3)
- >> (SCHED_CAPACITY_SHIFT-1)) + 1;
-
- if (cap_from_dt)
- topology_normalize_cpu_scale();
-}
-
-/*
- * Look for a customed capacity of a CPU in the cpu_capacity table during the
- * boot. The update of all CPUs is in O(n^2) for heteregeneous system but the
- * function returns directly for SMP system.
- */
-static void update_cpu_capacity(unsigned int cpu)
-{
- if (!cpu_capacity(cpu) || cap_from_dt)
- return;
-
- topology_set_cpu_scale(cpu, cpu_capacity(cpu) / middle_capacity);
-
- pr_info("CPU%u: update cpu_capacity %lu\n",
- cpu, topology_get_cpu_scale(NULL, cpu));
+ topology_normalize_cpu_scale();
}

#else
static inline void parse_dt_topology(void) {}
-static inline void update_cpu_capacity(unsigned int cpuid) {}
#endif

/*
@@ -276,8 +154,6 @@ void store_cpu_topology(unsigned int cpuid)

update_siblings_masks(cpuid);

- update_cpu_capacity(cpuid);
-
pr_info("CPU%u: thread %d, cpu %d, socket %d, mpidr %x\n",
cpuid, cpu_topology[cpuid].thread_id,
cpu_topology[cpuid].core_id,
--
2.11.0
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